Intel-Backed Chip Tech Deliberately Gets It Wrong

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In 1994, a flaw in the lookup table used by Intel’s Pentium floating-point unit produced seemingly random errors. Now, fifteen years later, computing errors are being used for a sort of “good-enough computing” that could promise dramatically reduced power consumption.

At the International Solid-State Circuits Conference Monday morning on San Francisco, a team of Rice University researchers will unveil a type of chip called “probabilistic CMOS, or PCMOS, which promises to be about seven times faster than conventional CMOS. The team’s research was funded by Intel as well as DARPA, the Defense Advanced Research Projects Agency.

According to the team, conventional CMOS has been constantly improved by increasing the chip’s operating voltage to reduce errors. The tradeoff is increased power.

In certain environments, however, probabilistic logic assumes that some errors will be accepted by a user as a tradeoff for dramatically lower power: in mobile video, for example, users might accept some video artifacts caused by errors introduced in the calculation of the algorithm. Another application may be encryption, which embraces random errors to improve the complexity of the encryption algorithm.

A PCMOS-based ASIC was jointly validated by Rice and Nanyang Technological University (NTU) in Singapore via a joint institute that Rice University professor Krishna Palem founded in 2007, the Institute for Sustainable Nanoelectronics (ISNE). ISNE is based at NTU, where the first prototype PCMOS chips were manufactured last year in collaboration with Professor Yeo Kiat Seng and his team, Rice University said in a statement.

The university did not release any information about the actual power saved by the test chips, or the scope of the errors.

Meanwhile, Intel’s Pentium floating-point bug did not technically produce random errors; according to the company’s official explanation of the bug, certain entries from a lookup table were omitted, which generated a higher probability of errors in certain cases. “Encountering the problem is highly dependent upon the input data,” Intel stated.

Intel believes that probabilistic logic could play a role in future semiconductor design, however.

“Coupled with the significant energy and speed advantages that PCMOS offers, this logic will prove extremely important because basic physics dictates that future transistor-based logic will need probabilistic methods,” said Shekhar Borkar, an Intel Fellow and director of Intel’s Microprocessor Technology Lab, in a statement.

The Rice-NTU team plans to follow its proof-of-concept work on encryption with proof-of-concept tests on microchips for cell phones, graphics cards and medical implants, the university said. The PCMOS technology could be made into products in as little as four years.